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Vagrant

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Johannes Schindelin edited this page Jan 28, 2014 · 7 revisions

Introduction

Vagrant is a modern way to define the requirements of a project. In the case of msysGit, it allows us to set up a minimal virtual Linux machine for trying out/using Linux Git on Windows without much effort.

Note: while Vagrant makes things easy, quite a bit of bandwidth is required for the initial steps: in total, roughly a gigabyte will need to be downloaded to get started.

How to install

  1. Download and install VirtualBox
  2. Download and install Vagrant
  3. Run vagrant up in the /git/ directory of msysGit
  4. Run vagrant ssh

Note that the prompt shows that the current directory in the ssh session inside the virtual machine is /vagrant/git and that the files in that directory are suspiciously identical to the /git/ directory in your msysGit installation. This is not by accident. In fact, the /vagrant/git directory inside the virtual machine is the /git/ directory of the hosting msysGit.

Why?

Git was invented to work with Linux. Over the years, it has become more and more platform-independent, but still support for Linux outshines support for every other platform, including Windows. Therefore it is preferable under certain circumstances to run Git inside Linux in a virtual machine, for example

  • for finding out whether a bug is Windows-specific or not
  • for performance (Linux' filesystem and memory management is better than Windows')
  • for proper 64-bit support (msysGit -- as of 1.8.5.2 -- does not support 64-bit binaries)
  • for current Subversion bindings (it is notoriously hard to compile Subversion bindings into MSys' Perl)
  • etc

Known problems

  • The Linux version of Git was designed to run on Linux file systems. Vagrant exposes msysGit's root directory as /vagrant/ but of course it cannot make up for the Windows file system's lack of support for Unix-style file permissions nor case-sensitive file names. As a consequence, quite a few of the unit tests fail when run in-place.
  • Git cannot be built with Perl's MakeMaker using Vagrant: it tries to create files with double colons in their name (e.g. Git::I18N.3pm) which is not allowed on Windows file systems.
  • If msysGit was started inside a VirtualBox (e.g. to be able to test Git for Windows even on a Linux/MacOSX laptop), VirtualBox will not be able to start the virtual machine (with an error message VERR_VMX_NO_VMX). This is a known problem with VirtualBox.
  • git svn is very slow. Actually, git svn is not very slow. But it is if you run it inside a directory under /vagrant/. The reason is that Linux' superior file system performance cannot come to full play when accessing /vagrant/ -- which really is the msysGit root directory managed by Windows. If you want to benefit from Linux' performance characteristics, you will have to perform the time-critical operations either in /home/vagrant/ inside the virtual machine, or inside a tmpfs.

Tips & Tricks

Use tmpfs

Linux offers a plethora of file systems optimized for different use cases. One of them is tmpfs, a RAM-based file system which keeps all files in virtual memory and is therefore very fast (but does not persist any of the data to disk).

Using such a file system can speed up Git operations quite substantially, in particular when performing disk-intensive operations, such as git filter-branch, git gc or git svn. It is very easy to create a tmpfs-backed file system:

mkdir -p $HOME/tmp
sudo mount -t tmpfs -o size=10G tmpfs $HOME/tmp
cd $HOME/tmp

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